This invention relates to the eductor used in hydraulic processing (dredging) of placer deposits for the recovery of values therein, usually gold. A good up-to-date description of gold dredging in all of its aspects including equipment, is to be found in Matt Thornton's book: "Dredging for Gold", first printing 1975. The suction gold dredge is described and illustrated on pages 31 to 35 in the 3rd printing (1979) version.
On p. 35, the beginning with par. 3 and continuing to the middle of p. 37, the author discusses the basic "power jet" or eductor as being widely used since the late `60`s; however, in the past few years, some manufacturers have developed interesting variations on the original theme. Perhaps the most significant is known as a "four eductor", or "four banger" power jet. Instead of using a single orifice assembly welded onto the straight metal tube, the 4-eductor jet, as the name implies, has 4 orifices assemblies; these are spaced 90.degree. apart on the outside surface of the metal tubing, all of them the same distance from the end of the tube where the suction hose is clamped on. All 4 orifice assemblies are fed by a single "water manifold", which is around, enclosed chamber encircling the straight metal tube, with openings into the 4 eductors. The pressure hose from the dredge's pump output is coupled to the water manifold. When the dredge engine is started and the manifold fills with water, 4 jet streams--all equal in velocity and pressure--shoot into the straight metal tube. The "quadradial" jetting arrangement serves to distribute the physical wear equally throughout all parts of the jet tube, resulting in longer "jet life".
The device of the present disclosure is an improvement on the device described above in the direct-quoted words of Thornton. In the Thornton device the four jet nozzles must be joined each at one end to the eductor tube and at the other end to the manifold ring by welding together the separate metal elements. The intricate assembly is a welder's nightmare. The finished eductor is a heavy, expensive, one-piece assembly with a relatively short service life in the wet, abrasive, corrosive environment of its use. The jets cannot be quickly interchanged with others of the same or different bore. Instead, the entire eductor assembly must be replaced.
The improved eductor of this invention consists essentially of two separate parts: (1) a manifold ring provided with a plurality, preferably four, of radially-spaced, forwardly- and convergingly- directed jet nozzles and, (2) a tube having a bell end, near the bell end at a fixed axial distance therefrom a number of peripheral bosses, radially disposed and equal in number to said plurality of nozzles. Each boss contains a forwardly- and convergingly- directed porthole adapted to snugly receive a corresponding one of the jet nozzles.
Each of the two parts of the eductor assembly is made of viscoelastic polymer, a material uniquely characterized by having a "memory" whereby it is capable of reverting in due time to its original shape, length or configuration after transitory bending or stretching.
The "memory" is utilized when the eductor is assembled by forcing the nozzle tips of the manifold ring over the bell end of the tube into registry with corresponding portholes. The nozzle tips in the original as cast configuration are exteriorly tangent to an inscribed circle of a diameter which is substantially less than the outside diameters of the bell end and of the inscribed circle of the portholes. Accordingly, the nozzle tips are forcibly bent divergingly to register with the portholes. As the nozzle tip enters the porthole the penetrated portion of the nozzle shank must thereafter bend convergingly, i.e., it must negotiate snake-like a divergent-convergent or S-curve flexure. As the penetration continues to advance by forced coaxial translational motion of the manifoild ring over the tube, a point is reached where the bending stresses vanish, the nozzles straighten out and revert to their original as cast configuration coaxially aligned within their corresponding portholes. For the purpose of this disclosure we designate this critical extent of penetration as the "home position."
The dimensions and the angle of convergence are carefully selected so that in the home position the tip of the nozzle is slightly outside of the inside diameter, or throat, of the tube. This allows about 0.125" for fine adjustment of the manifold ring by coaxial translational motion forward or reverse from the home position to optimize the suction performance of the eductor. It is not recommended, however, to advance the ring past the point where the nozzle tip enters the throat of the tube. This introduces a restriction in the throat where large size rock will be intercepted, causing blockage. Furthermore, the nozzle tips would be exposed to undesirable abrasion and wear.
The snake-like flexure mechanism of the nozzle described above is not actually the sole active deforming participant. It should be understood that other elements of the manifold ring and of the eductor tube cooperatively deform with the nozzles under the stress and revert to their original as cast configuration upon relief of the stress. For example, the conical base of each nozzle is joined to the forward face of the manifold ring which face it subjects to buckling deformation by leverage action of the force applied to the nozzle, while the nominally circular body of the manifold ring itself is pulled outwardly toward the corners of an n-polygon, where n designates the number in said plurality of jet nozzles. The stress on the eductor tube circular cross-section is equal and opposite to that on the manifold ring. When the circular tube is subjected to complementary inwardly-directed forces its circular shape tends to be dimpled into a rose of n-petals, but these distortions are imperceptibly small. The extent to which each of the elements contribute to the total viscoelastic deformation is not known. Let it suffice for the purpose of making this disclosure to attribute the distortion exclusively to the nozzle, i.e., the shank of the nozzle, and to consider all of the other elements to be rigidly unyielding and undeformed during the process of assembly and/or dissasembly. The term: "transitory snake-like flexure" hereinafter applied to the nozzle or the shank of the nozzle accordingly, is intended to embody the total aggregate viscoelastic distortion of all participating elements of the eductor.
It is an object of the invention to provide a two part multiple jet eductor which can be discussed and re-assembled easily and quickly in the field, replacing either part as necessary with an interchangeable part.
It is another object to provide a multiple jet eductor having improved resistance to abrasion and wear for a longer useful life.
It is still another object to provide a multiple jet eductor constructed of non-rusting, corrosion resistant material.
It is still another object to provide a multiple jet eductor constructed of material having high lubricity and non-galling characteristics, with a natural resistance to dents and permanent deformation, which is resilient to the impact of ingested rocks, whereby oversize rocks wedged in the throat of the eductor are dislodged by momentary ovalization of the bore under the imposed wedging stress.
It is still another object to provide a multiple jet eductor which is about 75% lighter and more compact than present all metal welded eductors of the same nominal throat diameter and of more compact configuration thereby to reduce the effort and space needed to haul and backpack it into remote mountain streambed destinations.
It is still another object to provide a multiple jet eductor which is more maneuverable in fast water currents for an operator balancing with insecure footing on sharp or slippery submerged rocks.
It is still another object to provide a multiple jet eductor having latitude for fine adjustment of the position of the jet nozzle tip relative to its angle of convergence in the throat so as to maximize the performance in eduction.
It is still another object to provide a multiple jet eductor having a size-stepped water inlet adapted to receive pressure water hoses in a variety of sizes.
It is still another object to provide a multiple jet eductor which is provided with a water hose stub directed forwardly and/or one that is directed rearwardly for the optional attachment of a length of hose used for flushing away lighter sediments overlying the values, particularly in cavities and in interstices between large rocks.
It is still another object to provide a multiple jet eductor having thread lugs in the inside diameter of the bell end to threadably receive and secure one end of the spiral wound flexible suction hose.
These objects are successfully embodied in the herein disclosed device.